net: dsa: sja1105: Reverse TPID and TPID2

>From reading the P/Q/R/S user manual, it appears that TPID is used by
the switch for detecting S-tags and TPID2 for C-tags.  Their meaning is
not clear from the E/T manual.

Signed-off-by: Vladimir Oltean <olteanv@gmail.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>